A conventional known technology is a technology of measuring the numerical value information on the subject substance in the body fluid, e.g., measuring continuously a glucose concentration in an interstitial liquid of the examinee by employing an electrochemical sensor embedded in an abdomen region and an arm region of the examinee. The electrochemical sensor is a sensor capable of detecting a minute amount of electric current by making use of electrochemical reaction, and is suited to detecting a minute amount of chemical substance in which oxidation-reduction reaction occurs.
The electrochemical sensor for measuring the glucose concentration involves using, in many cases, a biosensor which detects the subject substance by utilizing enzyme reaction in a way that immobilizes the enzyme to a sensor unit so disposed as to be embedded subcutaneously. This type of biosensor normally has a working electrode and a counter electrode, in which the enzyme (e.g., glucose oxidase) is immobilized to the working electrode. The glucose concentration can be measured based on, with a constant voltage (e.g., approximately 0.3V-0.6V) being consecutively applied to between the working electrode and the counter electrode, a response current obtained at this point of time.
The glucose oxidase produces gluconic acid by selectively reacting on the glucose under an existence of oxygen. On this occasion, the oxygen is reduced, while hydrogen peroxide proportional to a quantity of the glucose is generated. The hydrogen peroxide can be oxidized electrochemically easily and can be therefore measured by use of a pair of electrodes. Namely, the response current value can be obtained by the electrochemically oxidizing the hydrogen peroxide generated by the enzyme reaction of the enzyme as described above. Then, the glucose concentration can be calculated based on a sampling current obtained by periodically sampling the electric current from the continuously acquired response current values.
An activity of the enzyme, however, fluctuates depending on a reaction temperature. By contrast, a subcutaneous temperature largely fluctuates depending on a change in heat up temperature environment surrounding the examinee such as a living environment (e.g., an outdoor air temperature) of the examinee and activities in daily living (typified by bathing and taking excises) thereof. Therefore, in the case of continuously measuring the glucose concentration over a comparatively long period of time by use of the subcutaneous-embedding type of electrochemical sensor, a measurement result thereof is easily affected particularly by the change in heat up temperature environment.
Hence, in the case of measuring the glucose concentration by employing the subcutaneous-embedding type of electrochemical sensor, there is proposed a technology of measuring a temperature ambient to the sensor unit as the reaction temperature and correcting a calculated value corresponding to the measured temperature (refer to U.S. Pat. No. 6,560,471).
This type of temperature correction is normally conducted by use of temperature correction data indicating temperature dependency that is empirically obtained beforehand. The temperature correction data is used for determining a correction quantity and a correction coefficient on the basis of a temperature difference between a normal temperature and an ambient temperature in a way that sets the normal temperature (e.g., about 25° C.) as a reference temperature and for canceling the influence caused by the change in heat up temperature environment surrounding the examinee on the basis of this correction quantity.